Device for turning on light and illumination apparatus

ABSTRACT

A device for turning on light allowing the brightness of an inverter-type illumination apparatus to be adjusted without having to install an additional oscillation circuit. The device comprises an active converter which generates a DC voltage from the commercial AC voltage and an inverter which switches the generated DC voltage, includes a capacitor connected in parallel with a discharge tube to be lighted, and supplies a high-frequency current to the discharge tube via a resonance circuit whose resonance frequency is determined according to the equivalent impedance of the discharge tube. The active converter has a triac adjusting the DC voltage, and switching elements of the inverter perform self-oscillation under control of the phase of the resonance current flowing through the resonance circuit.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a device for turning on light,and more particularly to an inverter-type device for turning on lightand an inverter-type illumination apparatus.

[0002] Recently, an inverter-type illumination apparatus, which convertsthe DC voltage obtained from the commercial AC voltage to ahigh-frequency AC voltage for application to a discharge tube, has beenwidely used. The discharge tube of this illumination apparatus may be astandard fluorescent lamp with a filament or a non-electrode fluorescentlamp without a filament in which a plasma is generated by the line ofmagnetic force emitted from an excitation coil. It is known that thistype of inverter-type illumination apparatus has a light adjustmentfunction. For example, the circuit for turning on light disclosed inJP-A-8-37092 changes the frequency of the AC current, supplied to theresonance circuit, to change the amount of current flowing into thedischarge tube-for brightness adjustment.

[0003] The conventional device for turning on light described above usesa variable-frequency oscillation circuit, which generates the squarewave of a desired frequency, to change the frequency of the current tobe supplied to the resonance circuit. This additional circuit increasesthe number of parts and the cost. In addition, changing the frequency inorder to change the brightness of the illumination apparatus requiresthe user to operate the device for turning on light within theillumination apparatus. Therefore, the brightness of the illuminationapparatus cannot be adjusted remotely.

SUMMARY OF THE INVENTION

[0004] It is an object of the present invention to provide a function toadjust the brightness of an inverter-type illumination apparatus withouthaving to install an additional oscillation circuit. It is anotherobject of the present invention to provide a function to remotely adjustthe brightness of an inverter-type illumination apparatus.

[0005] The above objects are achieved by a device for turning on lightcomprising DC (Direct Current) voltage generating means for generating aDC voltage from a commercial AC (Alternate Current) voltage; and firstswitching means for switching the generated DC current and for supplyinga high-frequency current to a discharge tube via first resonance circuitmeans which includes a capacitor connected in parallel with thedischarge tube to be lighted and whose resonance frequency is determinedaccording to an equivalent impedance of the discharge tube, wherein theDC voltage generating means has control means for adjusting a value ofthe DC voltage and wherein a switching of the switching means iscontrolled by a phase of a resonance current flowing through the firstresonance circuit means.

[0006] When the DC voltage supplied to the first switching means ischanged to change the amplitude of the high-frequency AC voltage in thedevice for turning on light, the value of the current flowing throughthe discharge tube also changes. Because the discharge tube has negativeresistance characteristics, the equivalent impedance of the dischargetube also changes. Therefore, the resonance frequency of the firstresonance circuit changes accordingly, the switching frequency of thefirst switching means changes, and the frequency of the AC currentflowing through the first resonance circuit changes. When the frequencyof the AC current changes, the impedance of the capacitor in parallelwith the discharge tube changes, the ratio between the current flowingthrough the discharge tube and the current flowing through the capacitorchanges, and the brightness of the discharge tube changes. That is,simply changing the DC voltage to be supplied to the first switchingmeans automatically changes the frequency of the high-frequency ACcurrent supplied to the resonance circuit and the discharge tube,changing the current flowing through the discharge tube, thus changingthe brightness. Therefore, an additional oscillator defining theswitching frequency of the switching means required in the conventionaldevice is no more needed.

[0007] The first switching means comprises two switching elements whichare alternately conducted or non-conducted when a control signalobtained from the resonance current flowing through the first resonancecircuit means is applied, the two switching elements connected inseries; and means for changing a phase of the control signal.Controlling the timing in which the switching elements conduct preventsthe switching elements from being heated by the charge and discharge ofthe parasitic capacitance.

[0008] The DC voltage generating means comprises a first capacitor whichreceives a current from the commercial AC voltage to establish the DCvoltage; and second switching means for supplying the current from thecommercial AC voltage to second resonance circuit means and for moving acharge accumulated in the second resonance means to the first capacitor,wherein the second switching means and the first switching means are thesame. This configuration enables the DC voltage supplied to theswitching means to be amplified.

[0009] The above objects are achieved by a device for turning on lightwith a communication function, comprising an inverter generating ahigh-frequency current from a commercial AC voltage supplied from a lampline and supplying the current to a discharge tube to be lighted; and acommunication interface communicating with external units via the lampline, wherein the inverter comprises DC voltage generating means forgenerating a DC voltage from the commercial AC voltage supplied from thelamp line; switching means for switching the generated DC voltage andfor supplying the high-frequency current to the discharge tube via aresonance circuit including a capacitor connected in parallel with thedischarge tube; and driving circuit means for controlling the switchingof the switching means based on a signal supplied from external sources,and wherein the communication interface comprises filter means forextracting from the commercial AC voltage an analog signal includinglighting control information and superposed on the commercial ACvoltage; means for generating a digital control signal sending at leastone of switching start information, switching stop information, andswitching frequency information to the driving circuit means based oninformation from the filter means; and lighting control means forsending the digital control signal to the driving circuit means.

[0010] Sending a signal from external units to this device for turningon light with a communication function allows the frequency of the ACvoltage applied to the discharge tube to be changed, thus making itpossible to remotely adjust the brightness of the discharge tube.

[0011] The inverter further comprises a first sensor generating lightingstate information as a digital lighting state signal and wherein thecommunication interface converts the digital lighting state signal,received from the first sensor, to an analog signal and superposes thesignal on the commercial AC voltage for transmission to external unitsvia the lamp line. In addition, the inverter further comprises a secondsensor detecting a presence of and a life running-down state of thedischarge tube and wherein the communication interface converts thedigital lighting state signal, including information detected by thefirst sensor and second sensor, to an analog signal, superposes thesignal on the commercial AC voltage, and transmits the signal toexternal units via the lamp line. This makes the management andmaintenance of the illumination apparatus more efficient.

[0012] The lighting control means further comprises storing means forstoring therein a control pattern controlling the discharge tube in sucha way that the discharge tube is lighted at a maximum luminous flux fora predetermined time after a start of lighting and, after thepredetermined time, at a luminous flux lower than the maximum luminousflux. This allows the user to use the illumination apparatus moreefficiently and reduces the power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a block diagram of a first embodiment of a device forturning on light according to the present invention.

[0014]FIG. 2 is a diagram showing the operation of the device forturning on light of the present invention.

[0015]FIG. 3 is a diagram showing the operation of conduction phaseangle control of a dimmer.

[0016]FIG. 4 is a diagram showing the waveforms indicating the relationbetween the dimmer output voltage of the conventional device for turningon light and the DC voltage supplied to an inverter.

[0017]FIG. 5 is a circuit diagram showing the device for turning onlight in the first embodiment of the present invention.

[0018]FIG. 6 is a waveform diagram showing the voltage and the currentof the circuit shown in FIG. 5.

[0019]FIG. 7 is a graph showing the relation between the conductionphase angle of a dimmer and the DC voltage supplied to the inverter whenan active converter is used and when the active converter is not used.

[0020]FIG. 8 is a circuit diagram showing a device for turning on lightin a second embodiment of the present invention.

[0021]FIG. 9 is a graph showing the relation between the conductionphase angle of the dimmer, the DC voltage supplied to the inverter, andthe lamp power of the device for turning on light shown in FIG. 8.

[0022]FIG. 10 is a graph showing the relation between the lamp power andthe brightness of the lamp of the device for turning on light shown inFIG. 8.

[0023]FIG. 11 is a configuration diagram showing an illumination systemusing an illumination apparatus according to the present invention.

[0024]FIG. 12 is a waveform diagram showing a lighting control signalsuperposed on the commercial AC voltage.

[0025]FIG. 13 is a circuit diagram showing a first embodiment of thedevice for turning on light with a communication function according tothe present invention.

[0026]FIG. 14 is a circuit diagram of a filter circuit used in thedevice for turning on light shown in FIG. 13.

[0027]FIG. 15 is a circuit diagram showing a second embodiment of thedevice for turning on light with the communication function according tothe present invention.

[0028]FIG. 16 is a circuit diagram showing the details of a gate drivingcircuit of the device for turning on light shown in FIG. 15.

[0029]FIG. 17 is a circuit diagram showing a third embodiment of thedevice for turning on light with the communication function according tothe present invention.

[0030]FIG. 18 is a diagram showing a power circuit of the device forturning on light shown in FIG. 17.

[0031]FIG. 19 is a diagram showing a modification of the power circuitof the device for turning on light shown in FIG. 17.

[0032]FIG. 20 is a diagram showing an example of a lighting controlpattern of the device for turning on light with the communicationfunction according to the present invention.

[0033]FIG. 21 is a circuit diagram showing a fourth embodiment of thedevice for turning on light with the communication function according tothe present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0034]FIG. 2 is a block diagram showing the operation of a device forturning on light according to the present invention. A discharge tube 1may be a standard fluorescent lamp with a filament or an illuminationlamp, such as a non-electrode fluorescent lamp, without a filament inwhich a plasma is generated by the line of magnetic force emitted froman excitation coil. A control unit 6 superposes the control signal forbrightness adjustment on the commercial AC power AC. Upon detecting thecontrol signal, switching means 2 sends to an inverter 5 the DC voltageresponsive to the control signal or the signal to control the dischargetube 1.

[0035]FIG. 1 is a block diagram showing a first embodiment of the devicefor turning on light according to the present invention. The commercialAC power AC, phase-angle controlled by a dimmer 7 which is a controlunit, outputs the voltage only during the periods corresponding to theconduction phase angle indicated by the arrow in FIG. 3. The waveformindicated by the dotted line is the commercial power voltage input tothe dimmer 7. In FIG. 1, the voltage output from the dimmer 7 isrectified by a rectifier 3. The rectified voltage is transformed to avoltage responsive to the conduction phase angle, shown in FIG. 3, by anactive converter 4 which acts as switching means. The voltage applied tothe inverter 5 is a DC voltage obtained by the converter 4. The inverter5 transforms this DC voltage to a high-frequency AC voltage and appliesit to the discharge tube 1 to turn it on.

[0036] Because the conventional inverter-type circuit for turning onlight rectifies the commercial AC power AC with the rectifier 3 togenerate the DC voltage with a capacitor which smoothes the pulsatingcurrent, it acts as a capacitive impedance to the dimmer 7. Thus,immediately after the triac of the dimmer 7 is turned on, a rush currentsuddenly flows from the AC power AC, causing the dimmer 7 tomalfunction. FIG. 4 shows the waveforms of the output voltage of thedimmer in the conventional device for turning on light, input currentfrom the AC power, and DC voltage. When the DC voltage becomes lowerthan the output voltage of the dimmer 7, the rush current flows from theAC power. The problem is that, because the dimmer 7 does not operateproperly, the output voltage of the dimmer is not phase-anglecontrolled.

[0037] On the other hand, the device for turning on light with theconfiguration shown in FIG. 1 has the active converter 4 so that thecircuit for turning on light does not act as a capacitive impedance tothe dimmer 7. This configuration allows the input current with awaveform similar to that of the output voltage of the dimmer 7 to flow.Thus, the configuration implements a resistive load such as that of anincandescent lamp. At the same time, the configuration eliminates thedifference in phase between the voltage and the current and increasesthe power factor.

[0038]FIG. 5 is a circuit diagram showing the first embodiment of thepresent invention. Referring to FIG. 5, the voltage obtained byrectifying the AC power AC with the rectifier 3, composed of diodebridges, is converted to a DC voltage by the resonance-type activeconverter 4 via a low-pass filter composed of inductors L2 and L3 and acapacitor C4. The voltage is transformed by the inverter 5 to ahigh-frequency voltage and is supplied to the discharge tube 1 forhigh-frequency lighting.

[0039] The active converter 4 and the inverter 5 share twonon-complementary power semiconductor switching elements Q1 and Q2. Theswitching elements Q1 and Q2 are each an N-channel power MOSFET whichhas a drain terminal receiving the electric current, a source terminalsending the electric current, and gate terminal to which the controlvoltage is applied. Applying or not applying the control voltage to thegate terminal causes the electric current between the drain and thesource to flow or to stop, respectively. Each MOSFET, with a diodearranged in parallel from the source terminal to the drain terminal,allows the current to flow bi-directionally. In the description below,the diode contained in Q1 is called QD1, and the diode contained in Q2is called QD2.

[0040] In the active converter 4, diodes D1 and D2 are connected inseries in a forward direction between the contact between inductor L2and the capacitor C4 of the low-pass filter and the high-potential sideof a smoothing capacitor C1. In addition, a resonance circuit composedof a capacitor C2 and an inductor L1 connected in series is insertedbetween the contact between D1 and D2 and the contact between Q1 and Q2connected in the half-bridge structure.

[0041] The inverter 5 has the switching elements Q1 and Q2 between thepositive electrode and the negative electrode of the DC power. Betweenthe drain and the source of Q2, a series resonance circuit, which iscomposed of inductors L4 and LR and resonance capacitor CR connected inseries, is connected. The discharge tube 1 is connected in parallel withthe capacitor CR. Inductors L5 and L6 are feedback windings for theinductor L4. The inductor L5, provided in parallel with capacitor C5, isconnected between the gate and source of the switching element Q1, whilethe inductor L6, provided in parallel with capacitor C6, is connectedbetween the gate and source of the switching element Q2.

[0042] The switching elements Q1 and Q2 feed back the high-frequencycurrent flowing through the inductor L4 with the use of the inductors L5and L6 for self-oscillation. The inductor L4 may also be shared as aresonance inductor. The switching frequency of the inverter is sethigher than the resonance frequency determined by the resonance inductorLR and the resonance capacitor CR of the inverter 5. That is, theswitching frequency is set higher than the resonance frequency so thatthe phase of the resonance current lags behind that of the outputvoltage of the inverter.

[0043] As the switching frequency approaches the resonance point, theimpedance of the resonance circuit decreases to give a high voltagerequired to allow the discharge tube to keep on lighting. However, theself-oscillation inverter like this cannot change the switchingfrequency freely. Therefore, in this embodiment, the amplitude of the DCvoltage supplied to the inverter is changed to control the power of thedischarge tube and to change the brightness of the discharge tube. Forexample, as the DC voltage decreases, the resonance current decreasesand therefore the current flowing through the discharge tube decreases.Because the discharge tube has negative resistance characteristics, theequivalent resistance of the discharge tube increases as the currentdecreases. Because the discharge tube is connected in parallel with theresonance capacitor, the resonance frequency increases as the resistanceof the discharge tube increases. Therefore, the switching frequency ofthe self-oscillation inverter is automatically increased. This decreasesthe impedance of the resonance capacitor, increases the equivalentresistance of the discharge tube, changes the ratio between the currentsflowing through them, and changes the power of the discharge tube. Thatis, changing the DC voltage of the inverter automatically changes theswitching frequency, making it possible to control the power of thedischarge tube. Next, the active converter which controls the DC voltageaccording to the conduction phase angle of the dimmer will be described.

[0044] Alternately turning on and off the switching elements Q1 and Q2at a high frequency causes the current to flow from the AC power AC intothe inductor L1 and the capacitor C2 of the active converter 4, changesthe voltage of the connection point between diodes D1 and D2, andcharges the smoothing capacitor C1. Therefore, because the input currentflows according to the voltage of the commercial AC power, sending thehigh-frequency current, which flows in response to the switching, to thelow-pass filter makes the waveform of the input current similar to thatof the output voltage of the dimmer 7, as shown in FIG. 6. The DCvoltage applied to the inverter depends on the composite impedance ofthe inductor L1 and the capacitor C2 of the active converter 4.Therefore, decreasing the impedance allows the DC voltage to becomehigher than the output voltage of the dimmer as shown in FIG. 6.

[0045] In addition, the resonance frequency, which is determined by theinductor L1 and the capacitor C2, is set lower than the switchingfrequency of the inverter so that the phase of the resonance currentflowing through the active converter lags behind the phase of the outputvoltage of the inverter. The current charged in the capacitor C1 changesaccording to the conduction phase angle of the AC power voltage when itis controlled by the dimmer 7. Therefore, the DC voltage also changes,and the relation between the conduction phase angle and the DC voltageis as shown in FIG. 7.

[0046] The following describes the difference in the change in the DCvoltage between the conventional converter and the active converter usedin this embodiment. For example, when the conduction phase angle changesfrom 50° to 150°, the DC voltage of the conventional converter changesfrom V1 to V2 by ΔVa although the dimmer malfunctions. On the otherhand, the DC voltage of the active converter changes from V3 to V4 byαVb. The DC voltages V3 and V4 are higher than V1 and V2, respectively,and the voltage change ΔVb is higher than ΔVa. The use of the activeconverter prevents the malfunction of the dimmer and, in addition, makesthe DC voltage higher than the commercial AC power voltage. In thisembodiment, largely changing the change in the amplitude of the DCvoltage supplied to the inverter 5 largely changes the output power ofthe discharge tube. This enables the brightness of the discharge tube tobe largely changed according to the conduction phase angle of the AC.

[0047]FIG. 8 is a circuit diagram of a second embodiment of a device forturning on light according to the present invention. Referring to FIG.8, like reference numbers designate like components in FIG. 5, and theirdescription is omitted. In the second embodiment, an active converter 4and an inverter 5 share two complementary power semiconductor switchingelements Q1 and Q3. Unlike those in the first embodiment, the switchingelement Q1 is an N-channel power MOSFET, and switching element Q3 is aP-channel power MOSFET. They are complementary. A feedback diode(hereafter called QD1) is contained between the source terminal and thedrain terminal of Q1. A feedback diode (hereafter called QD3) iscontained between the drain terminal and the source terminal of Q3. Thesource terminals of the switches Q1 and Q3 are connected by the commonconnection point S. The gate terminals are connected by the connectionpoint G. The current flowing between the drain and the source of Q1 andQ3 is controlled by the same voltage between the connection point G andthe connection point S.

[0048] Between the connection point S and the negative electrode of acapacitor C1, a capacitor Cf and a resonance load circuit including aresonance inductor LR, resonance capacitor CR, and DC component removingcapacitor Cd are connected. A discharge tube 1 is inserted in parallelwith the CR. The capacitor Cd of the resonance load circuit need not beincluded. In addition, the resonance load circuit may be connectedbetween the connection point S and the positive electrode of thecapacitor C1. The frequency of the current flowing through theseresonance load circuits depends on the values of the elements.

[0049] Alternately turning on and off the switching elements Q1 and Q3causes the current to flow bi-directionally in the resonance loadcircuit, and the discharge tube to turn on. A capacitor C7 connectedbetween the drain and the source of the switch Q1 adjusts the change inthe voltage across the drain and the source of both switches. Tcapacitor C7, if connected between the drain and the source of Q3, mayperform the same function.

[0050] The gate driving circuit controlling the conduction state of theswitches Q1 and Q3 includes the capacitor Cf connected to the resonanceload circuit. The capacitor Cf gets the driving voltage from the currentflowing through the resonance load circuit to cause the gate drivingcircuit to operate. With one end of the capacitor Cf as the point F, aninductor Lg and a capacitor Cs are connected between the connectionpoints G and F. The inductor Lg generates a phase difference in thevoltage across the gate and the source for the current flowing throughthe resonance load circuit. The capacitor Cs removes the DC componentsuperposed on the AC voltage applied between the gate and the source.

[0051] Zener diodes ZD1 and ZD2, opposed each other and connected inseries, are provided in parallel between the gate and the source. Thesediodes prevent the elements from being destroyed when an over-voltage isapplied across the gate and the source of the switching elements Q1 andQ3. In addition, a capacitor Cgs is connected between the gate and thesource to adjust the change in the voltage across the gate and thesource. That is, when alternately turning on and off the switches Q1 andQ3, this capacitor compensates for the dead time from the moment oneswitch is turned off to the moment the other switch is turned on. Thecurrent flowing through the switches Q1 and Q3 is the composite of thecurrent flowing through the resonance load circuit and the currentflowing through the active converter. Because the current flowingthrough the active converter changes in response to the voltage of thecommercial AC power, the current of the switches Q1 and Q3 also changes.This affects the amount of the current that is cut off when the gatevoltage of the switches Q1 and Q3 falls below the threshold and theswitches are turned off. Because this current charges or discharges theparasitic capacitance of the switches Q1 and Q3 and the capacitor C7after the switches are turned off, the time at which the voltage acrossthe drain and the source of the switches changes to the positivepotential or negative potential of the DC power voltage varies. When thegate voltage exceeds the threshold of the switches and the switches areturned on while the voltage across the drain and the source changes, athrough current flows along the path including the capacitor C7 andswitch Q1 or Q3, generating heat in the switch. In this embodiment, thedriving circuit composed of the capacitors Cf and Cgs and inductor Lggives an appropriate phase difference to the gate voltage of the switchto control the time at which the switches are turned on. This phasedifference, given according to the change in the load resonancefrequency or the amount of the current flowing through the switch,prevents the through current.

[0052] In FIG. 8, as the voltage of the AC power AC increases duringstartup and the DC voltage of the capacitor C1 increases, the currentflows along the path composed of a resistor R1 connected between thedrain and the gate of Q1, the inductor Lg, the capacitors Cs and Cf, anda resistor R2 connected between the source and the drain of Q3. Thiscurrent gradually increases the voltage at the connection point G, thatis, the voltage between the gate and the source. As the voltage acrossthe gate and the source exceeds the threshold voltage of the switchingelement Q1, Q1 is turned on. Then, the current flows from the connectionpoint S to the connection point F, thus decreasing the voltage at theconnection F. This makes the voltage across the gate and the sourceimmediately fall below the threshold voltage of Q1, turning off Q1. Atthis time, because the capacitor Cf connected between the connectionpoints F and S, the capacitor Cgs, and the inductor Lg form the LCresonance circuit, a slight change in the voltage of the capacitor Cfincreases the current flowing through the LC resonance circuit and,therefore, increases the amplitude of the voltage across the gate andthe source. This oscillation starts the switching operation in which theswitches Q1 and Q3 are turned on and off alternately. As in the firstembodiment described above, alternately turning on and off the switchingelements Q1 and Q3 at a high frequency causes the current to flow fromthe alternate current power AC into the active converter 4. This currentcharges the capacitor Cl according to the output of the dimmer 7 andcontrols the DC voltage.

[0053]FIG. 9 shows the relation between the DC current and the lamppower with respect to the AC conduction phase angle in the embodimentshown in FIG. 8. Referring to FIG. 9, the DC voltage gradually decreasesas the conduction phase angle decreases and, as the voltage decreases,the lamp power decreases. The relation between the lamp power and thebrightness of the lamp is shown in FIG. 10. As the lamp power decreasesfrom 18W to 6W, 100% of the brightness at 18W decreases to 40% at 6W. Inthe second embodiment, the conduction angle of the commercial AC poweris controlled by the dimmer described above. Even when the conductionphase angle control signal is superposed on the lamp line, it ispossible to adjust the output power of the discharge tube according tothe phase angle control signal.

[0054]FIG. 11 is a configuration diagram of an illumination systemconfigured by the illumination apparatus of the present invention. Thisfigure shows an illumination system which superposes the lightingcontrol signal on the commercial AC voltage supplied by a power company40 via a lamp line 41, as shown in FIG. 12, to control a plurality ofdevices for turning on light 100-103 connected to the lamp line. In FIG.11, a gateway 42 connected to the lamp line between the power companyand the power user functions as an interface via which the power companymonitors the amount of power used by power users and controls the amountof power. The control unit 6 connected in series to the lamp linebetween the gateway 42 and connection units 90-93 functions as a centralterminal controlling the devices for turning on light. The devices forturning on light 100-103 are connected to the connection units 90-93.

[0055] The connection units 90-93 each have a unit in which theconnection unit installation position is stored. This positioninformation allows the control unit 6 to identify the location of eachconnection unit. Superposing this position information on the controlsignal allows the devices for turning on light to be controlledindividually. Upon detecting that a device for turning on light isconnected, each connection unit sends the signal to the control unit 6.This signal enables the control unit to determine if a device forturning on light is connected.

[0056] An electrical apparatus 43 for adjusting the brightness of theillumination apparatus is connected to the lamp line 41. This electricalapparatus 43 is able to transfer information to or from the devices forturning on light 100-103 via the control unit 6. A device for turning onlight with a communication function to communicate via the lamp line 41in such a system described above will be described below.

[0057]FIG. 13 shows a first embodiment of a device for turning on lightwith the communication function which may be used in the illuminationsystem described above. An inverter 5 comprises two non-complementarypower semiconductor switching elements Q1 and Q2, a resonance circuit 5b, and a gate driving circuit 5 a which controls the conduction state ofthe switches. The device for turning on light in this embodiment has acommunication interface 2 which comprises coupling capacitors 22, afilter circuit 2 a, a signal amplifier circuit 2 b, amodulation/demodulation circuit 2 c, and a lighting control circuit 2 d.This interface sends and receives the control signal to or from thecontrol unit 6.

[0058] The coupling capacitors 22 electrically separate the lamp lineand the communication interface. The coupling capacitors 22 may bereplaced with coupling transformers. The filter circuit 2 a included inthe communication interface 2 is a band through filter which passes onlythe signal in the frequency band used by lamp line communication andremoves the signal outside the band. As shown in FIG. 14, this filtermay be monolithic, for example, when combined with a switched capacitorfilter comprising capacitors 23 and 25, a switch 27, and anope-amplifier 26.

[0059] The signal amplifier circuit 2 b amplifies the signal to ensurethat the information intelligent when the signal attenuates whilepropagating through a long line between the control unit 6 and thedevice for turning on light. The circuit also amplifies the signal whenthe signal is superposed on the Ac voltage sent from the device forturning on light to the lamp line. The modulation/demodulation circuit 2c demodulates the analog signal sent from the lamp line via the filtercircuit 2 a and signal amplifier circuit 2 b, or modulates the digitalsignal and outputs the analog signal. The lighting control circuit 2 ddecodes the digital signal output from the modulation/demodulationcircuit 2 c. For example, upon receiving a command that darkens thedischarge tube to 80%, the circuit outputs the control signal toincrease the switching frequency of the inverter. When the signalindicating the state of the inverter is sent from the gate drivingcircuit 5 a, the lighting control circuit decodes the signal and outputsthe digital signal to the modulation/demodulation circuit 2 c.

[0060] The gate driving circuit 5 a sends the driving signal to theinverter to drive the high-side and low-side switching elements Q1 andQ2. This driving circuit has a level-shift circuit that converts thedriving signal which uses the low-side element as the referencepotential to the driving signal which uses the high-side element as thereference potential. In addition, the gate driving circuit 5 a containsan oscillator which controls the switching frequency of the inverterbased on the control signal from the lighting control circuit 2 d. Atthe same time, the gate driving circuit sends switching frequencyinformation to the lighting control circuit 2 d to inform it whether theinverter is turned on.

[0061]FIG. 15 shows a second embodiment of a device for turning on lightwith the communication function according to the present invention. Inthis embodiment, the inverter comprises complementary switches connectedbetween DC power sources with the reference potential of the switchcontrol signal different from that of the DC power source. The referencepotential of the gate driving circuit of such complementary switchesconstantly varies. To send the signal to the driving circuit, the signalsending side and the signal receiving side must be electricallyseparated.

[0062] The device for turning on light in this embodiment comprisescoupling capacitors 22 such as those shown in FIG. 13 and acommunication interface 2 comprising a filter circuit 2 a, signalamplifier circuit 2 b, modulation/demodulation circuit 2 c, and lightingcontrol circuit 2 d. Between the inverter controller including a gatedriving circuit 5 a and the communication interface 2 are providedisolators 24 that electrically separate signals for transfer between theinverter controller and communication interface. The communicationinterface 2 is the same as the one described in FIG. 13 and thereforeits description is omitted.

[0063]FIG. 16 shows the circuit configuration of the gate drivingcircuit 5 a which drives complementary switches Q1 and Q3. To thecontrol node point G of the complementary switches Q1 and Q3 connectedbetween the positive potential and the negative potential of thesmoothing capacitor Cl, the output node of the CMOS transistor, composedof the p-channel transistor Q4 and the N-channel transistor Q5 connectedtogether via their drains, is connected. Similarly, to the referencenode S, the output node of the CMOS transistor, composed of theP-channel transistor Q6 and the N-channel transistor Q7 connectedtogether via their drains, is connected. The DC voltage is supplied fromthe nodes V1 and V1G to the CMOS transistors. The gate driving signal issent to the control input of each CMOS transistor from an oscillator 14via a buffer 15. The conduction state of the switching elements iscontrolled by this signal. The oscillator 14 receives a control signal20 from the lighting control circuit 2 d via the isolators 24 andgenerates a desired frequency to control the switching frequency. At thesame time, the oscillator outputs a state signal 21 indicating the stateof the inverter.

[0064] When a plurality of devices for turning on light must becontrolled speedily by the control unit 6 in FIG. 15, the signal mustalso be transmitted speedily between the communication interface and theinverter controller. The performance of the isolators 24 affects theresponsiveness of the devices for turning on light.

[0065]FIG. 17 shows a third embodiment of a device for turning on lightwith the communication function which has isolators satisfying thisrequest. In this embodiment, a control circuit 18 with a communicationinterface function similar to that in the embodiment described in FIG.15 and a drive circuit 17 with the inverter control function areprovided.

[0066] A complementary signal generator 18 e in the control circuit 18receives the digital signal from a lighting control circuit 18 d. Acomplementary signal generator 17 c in the drive circuit 17 receives thedigital signal from a gate driving circuit 17 a. These two signalgenerators generate signals 180° out of phase. The signals are input tocoupling capacitors 9 and 12 by driving circuits 8 and 11, and thecomplementary signals become differential waveform signals. Sensorcircuits 10 in the drive circuit 17 and sensor circuits 13 in thecontrol circuit 18 each detect the differential waveform and output thetiming information on the rise and the fall of the pulse. A flip-flop 17f in the drive circuit 17 and a flip-flop 18 f in the control circuit 18reproduce, respectively, the digital signals entered from the lightingcontrol circuit and the gate driving circuit based on the timinginformation from the sensor circuits 10 and 13. The reproduced digitalsignals are input to the gate driving circuit 17 a and the lightingcontrol circuit via buffers 17 g and 18 g.

[0067] The coupling capacitors 9 and 12 transmit signalsbi-directionally while electrically separating the communicationinterface and the inverter controller. The capacitor-implementedisolators like this, with the peripheral circuit configured by logicalcircuits, create a slight delay and therefore performs high-speedoperation.

[0068] The gate driving circuit 17 a driving the complementary switchesQ1 and Q3 is the same as that shown in FIG. 16. When the drive circuit17 has a discharge tube life detection circuit 17 b which detects thepresence and the life of the discharge tube, the gate driving circuit 17a stops the oscillator upon detection of the life running-down signalfrom the discharge tube life detection circuit 17 b, thus preventing theinverter from being damaged.

[0069] The conventional non-complementary switches, which require two180° out-of-phase control signals to drive the inverter, require alevel-shift circuit. Thus, the driving circuit is a high-voltagecircuit. On the other hand, the gate driving circuit of thecomplementary switches used in the embodiment described above is simple;that is, it comprises a CMOS transistor, oscillator, and buffer. Thissimple configuration allows the inverter to be controlled only by onecontrol signal. Therefore, the driving circuit, which is now alow-voltage circuit, may be built into an IC. In addition, thecapacitor-implemented isolators, which may be composed of logicalcircuits as described above, as well as the communication interface maybe mounted on the same wafer. Therefore, the part enclosed by a dottedline 16 shown in FIG. 17 may be implemented as a one-chip IC.

[0070] Next, with reference to FIG. 18, the power circuit supplyingpower to the drive circuit 17 and the control circuit 18 will bedescribed.

[0071] In FIG. 18, the reference potential of the gate driving circuitincluded in the drive circuit 17 is different from the voltage of thecapacitor C1, that is, the potential of the DC power. In the circuitshown in the figure, with a secondary winding L7 provided in theresonance inductor LR, the voltage of the secondary winding generated bythe resonance current flowing through the inductor LR is used. Thisvoltage causes the charge current to flow into a capacitor C8 via adiode D3. The voltage across C8, which is a DC voltage different fromthe voltage across C1, is supplied to the node points V1 and V1G of thedrive circuit 17. On the other hand, the reference potential of thecontrol circuit 18, which is the same as that of C1, is obtained byconnecting a resistor R3 and a capacitor C9 between the positive andnegative electrodes of C1 to charge C9 with the voltage of C1 togenerate a DC voltage. A zener diode ZD3 is provided in parallel with C9to regulate the voltage.

[0072] The reference potential of the control circuit 18 may bedifferent from that of C1, as in the drive circuit 17. In this case,another secondary winding L8 is provided for the inductor LR as shown inFIG. 19, and the generated secondary voltage is used. A capacitor C3 ischarged with this voltage via a diode D4, and the voltage across C3 issupplied to the node V2 of the drive circuit 17 and to the node V2G withthe reference potential that is different from that of C1. Duringstartup, the operation of the device for turning on light shown in FIG.18 is the same as self-oscillation described in FIG. 8. That is, theswitches Q1 and Q3 are alternately turned on and off to start theswitching operation. After startup, the current flows into the resonanceinductor LR to apply the DC voltage to the drive circuit 17, causing thedrive circuit 17 to start separately-excited drive operation.

[0073]FIG. 20 is a diagram showing an example of a lighting controloperation pattern in which the control unit controls the device forturning on light with the communication function described above. Whenthe device starts lighting at time t0, the mercury-vapor pressure insidethe discharge tube increases and, at the same time, the brightnessgradually increases. At time t1, the discharge tube reaches 100% offully-lighted state. Upon receiving an energy-saving operation modesignal from the control unit at time t2, the device for turning on lightcontrols the switching frequency of the gate driving circuit to keep ithigher than usual to slightly decrease the lamp power and maintains thebrightness about 80% of the fully-lighted state. In this energy savingmode, the brightness of the discharge tube is about 20% lower than thefully-lighted state. The brightness is decreased not suddenly butgradually to make the user feel that it does not get dark. At time t3when the control signal that further decreases the brightness of thedischarge tube is sent, the device for turning on light increases theswitching frequency to further decrease the lamp power for brightnessadjustment. Controlling the device for turning on light via the controlunit in this manner during the above-described energy-saving operationmode allows the brightness of the discharge tube to be adjusted to suchan extent that the user does not notice that it gets darker and, at thesame time, reduces the power consumption of the device for turning onlight. Information on the state of the discharge tube, for example,information whether the lamp is present or the lamp is running down,helps the user do maintenance work such as the replacement of dischargetubes.

[0074]FIG. 21 is a circuit diagram of a fourth embodiment of a devicefor turning on light with the communication function according to thepresent invention. The device for turning on light comprises a filtercircuit 51, a signal amplifier circuit 52, a modulation/demodulationcircuit 53, a lighting control circuit 54, a gate driving circuit 55,and a discharge tube life detection circuit 56. In the device forturning on light shown in FIG. 17, the isolators between thecommunication interface and the inverter controller uses capacitors. Inthis embodiment, a transformer 19 is used as the isolator. When thetransformer is used in this way, the lighting control circuit 54 in thecommunication interface decodes the digital signal from themodulation/demodulation circuit 53 and outputs the analog signalcorresponding to the signal to the transformer 19. When the inverterstate signal is sent from the inverter controller via the transformer19, the lighting control circuit decodes the analog signal and outputsthe digital signal to the modulation/demodulation circuit 53. The gatedriving circuit 55 receives the analog signal sent via the transformer19, generates a desired frequency, and controls the switching frequencyto adjust the brightness of the discharge tube 1. Upon receiving thesignal from the discharge tube life detection circuit 56, the gatedriving circuit stops oscillation to prevent the inverter from beingdamaged and, at the same time, outputs the analog signal correspondingto this state to the transformer 19.

[0075] The device according to the present invention allows thebrightness of an inverter-type illumination apparatus to be adjustedwithout having to install an additional oscillation circuit. Also, thedevice allows the brightness of an inverter-type illumination apparatusto be adjusted remotely.

[0076] While the preferred form of the present invention has beendescribed, it is to be understood that the present invention is notlimited to the embodiments but that modifications will be apparent tothose skilled in the art without departing from the spirit of thepresent invention.

What is claimed is:
 1. A device for turning on light comprising: DC(Direct Current) voltage generating means for generating a DC voltagefrom a commercial AC (Alternate Current) voltage; and first switchingmeans for switching the generated DC current and for supplying ahigh-frequency current to a discharge tube via first resonance circuitmeans which includes a capacitor connected in parallel with thedischarge tube to be lighted and whose resonance frequency is determinedaccording to an equivalent impedance of the discharge tube, wherein saidDC voltage generating means has control means for adjusting a value ofthe DC voltage and wherein a switching of said switching means iscontrolled by a phase of a resonance current flowing through said firstresonance circuit means.
 2. The device for turning on light according toclaim 1 wherein said first switching means comprises: two switchingelements which are alternately conducted or non-conducted when a controlsignal obtained from the resonance current flowing through said firstresonance circuit means is applied, said two switching elementsconnected in series; and means for changing a phase of said controlsignal.
 3. The device for turning on light according to claim 1 whereinsaid DC voltage generating means comprises: a first capacitor whichreceives a current from said commercial AC voltage to establish the DCvoltage; and second switching means for supplying the current from saidcommercial AC voltage to second resonance circuit means and for moving acharge accumulated in said second resonance means to said firstcapacitor, wherein said second switching means and said first switchingmeans are the same.
 4. The device for turning on light according toclaim 3 wherein a switching frequency of said first switching means ishigher than a resonance frequency of said second resonance circuit and,when there is no discharge tube, than the resonance frequency of saidfirst resonance circuit means.
 5. The device for turning on lightaccording to claim 1 wherein said control means for adjusting the valueof the DC voltage comprises an element controlling a conduction phaseangle of the AC power.
 6. A device for turning on light with acommunication function, comprising: an inverter generating ahigh-frequency current from a commercial AC voltage supplied from a lampline and supplying the current to a discharge tube to be lighted; and acommunication interface communicating with external units via the lampline, wherein said inverter comprises: DC voltage generating means forgenerating a DC voltage from the commercial AC voltage supplied from thelamp line; switching means for switching the generated DC voltage andfor supplying the high-frequency current to said discharge tube via aresonance circuit including a capacitor connected in parallel with saiddischarge tube; and driving circuit means for controlling the switchingof said switching means based on a signal supplied from externalsources, and wherein said communication interface comprises: filtermeans for extracting from the commercial AC voltage an analog signalincluding lighting control information and superposed on the commercialAC voltage; means for generating a digital control signal sending atleast one of switching start information, switching stop information,and switching frequency information to said driving circuit means basedon information from said filter means; and lighting control means forsending the digital control signal to said driving circuit means.
 7. Thedevice for turning on light with a communication function according toclaim 6, wherein said inverter further comprises a first sensorgenerating lighting state information as a digital lighting state signaland wherein said communication interface converts the digital lightingstate signal, received from said first sensor, to an analog signal andsuperposes the signal on the commercial AC voltage for transmission toexternal units via the lamp line.
 8. The device for turning on lightwith a communication function according to claim 7, further comprisingan isolator electrically separating said inverter and said communicationinterface.
 9. The device for turning on light with a communicationfunction according to claim 8, wherein said isolator comprisescapacitors or a transformer.
 10. The device for turning on light with acommunication function according to claim 7, wherein said lightingcontrol means and said gate driving circuit means comprise complementarysignal generating means generating two complementary signals, which are180° out of phase, and sending the signals as a control signal and alighting state signal respectively and means for reproducing the controlsignal and the lighting state signal from the received complementarysignals.
 11. The device for turning on light with a communicationfunction according to claim 10, further comprising capacitors separatingsaid inverter and said communication interface, wherein said means forreproducing comprises a pair of detection circuits getting informationon a rise and a fall of a pulse based on a differential waveform fromthe capacitors, a flip-flop reproducing the signal based on informationfrom said detection circuit, and a buffer temporarily storing thereinthe reproduced signal.
 12. The device for turning on light with acommunication function according to claim 7, wherein said inverterfurther comprises a second sensor detecting a presence of and a liferunning-down state of the discharge tube and wherein said communicationinterface converts the digital lighting state signal, includinginformation detected by said first sensor and second sensor, to ananalog signal, superposes the signal on the commercial AC voltage, andtransmits the signal to external units via the lamp line.
 13. The devicefor turning on light according to claim 6, wherein said lighting controlmeans further comprises storing means for storing therein a controlpattern controlling the discharge tube in such a way that the dischargetube is lighted at a maximum luminous flux for a predetermined timeafter a start of lighting and, after the predetermined time, at aluminous flux lower than the maximum luminous flux.
 14. An illuminationapparatus comprising: the device for turning on light according to claim6; and a connection unit connecting the device for turning on light tothe lamp line, wherein said connection unit comprises: storing meansstoring therein a position at which said connection unit is installed;and sending means for sending a signal indicating the installationposition over the lamp line.
 15. The illumination apparatus according toclaim 14 wherein said connection unit further comprises means forgenerating a signal indicating that the device for turning on light hasbeen connected and for sending the signal to said sending means.
 16. Theillumination apparatus according to claim 14 wherein said connectionunit further comprises means for generating a signal indicating acurrent supplied from the lamp line and for sending the signal to saidsending means.